I. Field of the Invention
The present invention relates to a process for impurity gettering in a semiconductor substrate or device such as a silicon substrate or device by first hydrogenating the substrate or device and thereafter thermally treating the substrate or device or illuminating the substrate or device with electromagnetic radiation in a manner conducive to cause the impurities to diffuse to the back side of the substrate or device for subsequent capture.
II. Description of the Prior Art
Gettering processes for removing impurities from a semiconductor substrate or device such as silicon substrate or device used for microelectronic devices have included phosphorous diffusion, chlorine treatment as with trichloroethane, and thermal treatments following specific methods of substrate surface damage. With respect to specific types of surface damage, Kramler et al., in U.S. Pat. No. 4,539,050, describe a technique for creating back-side wafer damage by laser irradiation. The damaged back side acts as a gettering region, and the wafer is treated thermally to generate dislocation networks responsible for gettering action. Hall et al., in U.S. Pat. No. 4,878,988, describe a process in which sawing produces surface damage which acts to trap impurities. Following a high-temperature treatment, the damaged surface is lapped to remove the gettered impurities. Sakata et al., in U.S. Pat. No. 5,051,375, produces back-side silicon wafer damage by means of sand blasting using a spherical abrasive. The sand-blasted wafer is then oxidized at a high temperature to produce gettering of impurities to the damaged surface. Thus, prior-art gettering procedures generally involve either severe chemical or severe physical treatment of silicon substrate.
The introduction of hydrogen ions into silicon substrates as a technique for the passivation of defects present in the substrates is described in U.S. Pat. No. 5,169,791 to Muenzer and in U.S. Pat. No. 5,304,509, incorporated herein by reference in its entirety, to Sopori. Muenzer describes a thermal treatment consisting of annealing a silicon wafer in a hydrogen-containing gas such as a hydrogen-oxygen mixture (e.g. water vapor). This thermal treatment results in a reduction of the hydrogen gas to atomic hydrogen which, in turn, diffuses into the wafer to passivate crystal defects. Sopori describes a technique to introduce hydrogen from the back side of a solar cell for passivation of impurities and defects. Hydrogen diffusion within the cell occurs via formation and diffusion of a hydrogen-vacancy (H-V) complex. After low-energy hydrogen implantation, the cell undergoes sequential low-intensity and high-intensity optical processing to dissociate the H-V complex, to release hydrogen for passivation, and to alloy the back side of the cell and form a silicon-aluminum alloy which also partially dissolves hydrogen-induced damage on the back side. During optical processing, some hydrogen-induced defects are annihilated. It may be pointed out that in the back side hydrogenation process of Sopori, the presence of surface damage and the hydrogen-induced defects can produce deleterious effects on device performance. Hence, the process described in the Sopori patent is designed to minimize residual defects produced by hydrogenation.
While Sopori teaches hydrogenation of silicon substrates followed by optical processing under specific intensity magnitudes, the disclosure does not teach parameters for impurity gettering through the use of hydrogenation followed by thermal treatment or optical processing. Accordingly, a primary object of the present invention is to provide a process for impurity gettering in a semiconductor substrate or device such as a silicon substrate or device wherein a surface of the substrate or device is first subjected to hydrogen-induced damage consisting of dislocations and platelets, with the substrate or device thereafter exposed to electromagnetic radiation such that impurities within the substrate or device are caused to diffuse to the damaged surface for subsequent capture.
Another object of the present invention is to provide a process for impurity gettering in a semiconductor substrate or device such as a silicon substrate or device wherein a surface of the substrate or device is first subjected to hydrogen-induced damage, with the substrate or device thereafter exposed to thermal treatment such that impurities within the substrate or device are caused to diffuse to the damaged surface for subsequent capture.
Yet another object of the present invention is to provide a process for impurity gettering and defect passivation in a semiconductor substrate or device such as a silicon substrate or device wherein a surface of the substrate or device is first subjected to hydrogen-induced damage while hydrogen atoms are implanted into the substrate or device, with the substrate or device thereafter exposed to electromagnetic radiation such that impurities and defects within the substrate or device are caused to diffuse to the damaged surface while substantially all hydrogen-induced damage on the damaged surface is simultaneously annihilated.
These and other objects will become apparent throughout the description of the invention which now follows.